Photometric indicators of headlamp performance.

695074662PDFTech ReportUMTRI-2009-18HeadlampsPhotometryMichiganUniversity of Michigan. Transportation Research InstituteSullivan, John M.Flannagan, Michael J.University of Michigan. Transportation Research InstituteNTL-SAFETY AND SECURITY-SAFETY AND SECURITYUS Transportation CollectionThe visibility of an object is largely determined by the relative contrast between theobject and its background. Thus, it might be assumed that without consideration ofenvironmental conditions surrounding a target illuminated by a headlamp, target visibility maynot be accurately assessed. That is, methods that consider only illuminance characteristics ofheadlamps (e.g., distribution and intensity of light) may assess headlamp performancedifferently from methods that include roadway and viewing conditions in the appraisal.In this report, headlamp performance ratings are first generated using CHESS, asoftware application that determines visibility by simulating headlamp illumination, roadway,and target characteristics, using target contrast. The CHESS ratings were then compared withratings obtained by two alternative illuminance-based ratings methods. The first method, thelux-area method, computes road area at or above an established lux threshold. The secondmethod, the distant-light method, computes the average lux level within a predefined forwardroad area centered on the midline of the vehicle. Twenty-two tungsten halogen (TH) headlampswere evaluated using each method and their performance ratings were compared with theCHESS ratings. The simple illuminance-based measures were found to be closely correlatedwith the CHESS ratings. The distant-light method produced the highest correlations